Coating method with precure and apparatus therefor

ABSTRACT

An apparatus and method are provided for producing a coating of heat fusible resinous material upon only a portion of a workpiece. The resinous material is deposited upon the workpiece as electrostatically charged particles. One zone of the workpiece is heated to cause fusion and cohesion of the particles while a second zone is simultaneously cooled to prevent such a result and to thereby facilitate removal of particles from the cooled zone. The apparatus and method are particularly adapted for producing thermoplastic coatings upon armature rotors for electric motors.

United States Patent Goodridge et al.

COATING METHOD WITH PRECURE AND APPARATUS THEREFOR Inventors: William C. Goodridge, West Haven; Donald J. Gillette, Guilford; William P. English, Bridgeport; G. Mark Minckler, Guilford, all of Conn.

Electrostatic Equipment Corporation, New Haven, Conn.

Filed: May 24, 1972 Appl. No.: 256,499

Assignee:

US. Cl 117/17, 117/8, ll7/17.5, 117/19,117/21,l17/38,ll7/93.1DH,

117/102 A, l17/l19.2, 118/624 Int. Cl..... 344d l/094, B44d l/095, B05b 5/02 Field of Search 1l7/8.5, 9, 17,175, 21, 117/38, 93.1 DH, 119.2, 119.4, 102 A; 118/624 References Cited UNITED STATES PATENTS 3/1961 Dettling 117/21 POWDER RECOVERY AND FEED [451 Feb. 11, 1975 3,377,183 4/1968 Hurt 117/17 3,440,078 4/1969 Sharetts 117/D1G. 6 3,695,909 lO/1972 Fabre et al.... 117/38 3,713,862 11/1973 Winkless ll7/17.5

Primary Examiner-Michael Sofocleous [57] ABSTRACT 12 Claims, 17 Drawing Figures POWDER REELENISH ELECTRIC INTERFACE NEL /ACCESS CHAN COATING PROCESS UNIT COOLING OVEN T P PATH-HEB M 11915 2. 865.610

SHEET l UF 7 PATENTEB FEB] 1:975

SHEET 5 BF 7 n III A u 1 COATING METHOD WITH PRECURE AND APPARATUS THEREFOR BACKGROUND OF THE INVENTION Of the various ways in which coatings of heat fusible resinous materials are produced upon various workpieces, those in which the material is applied in particulate or powdered form are often found to be the most effective and satisfactory. Such techniques are used to produce coatings upon a wide variety of workpieces, including continuous lengths of wire and strip stock as well as individual objects which are often of a complex configuration, as would make coating by other techniques difficult or impossible. For example, attempts have been made to insulate the slots of rotors and stators for electric motors by depositing the resin in powdered form, which has proven particularly difficult due to the presence of reentrant surfaces which must be covered.

A common method of producing coatings of thermoplastic particulate materials is to utilize heat from the workpiece to cause softening and fusion of the particles upon contact. Thus, it has long been the practice to heat the article and to then submerge it in a bed (desirably fluidized) of the particulate material so as to produce a coating upon all exposed surfaces, and as far as is known prior attempts to produce coatings from powdered resins upon electric motor components have employed this technique. However, the inherent drawbacks are quite apparent, and include the needfor masking of portions of the workpiece which are to remain free from the coating material and/or the need to handle or direct the resin in such a manner that contact will be avoided. Not only are such precautions time- 'consuming, but frequently they are difficult if not impossible to achieve in practice. Moreover, since the amount of material deposited using such a method is dependent upon the intensity of heat available from the workpiece and/or the duration of exposure, uniform thicknesses are oftentimes most difficult to obtain.

it is also well known that electrostatic forces may be utilized to cause attraction and adhesion of particles of thermoplastic materials to a wide range of workpieces, which may thereafter be heated to melt the resin and produce the final unified coating. This approach has many advantages including uniformity of coverage, ease of access to undercut or reentrant surfaces, coating thickness control, etc. Nevertheless, the production of preferential deposits upon selected areas of the object has typically relied upon the use of mechanical or air masking techniques which are not entirely satisfactory under certain circumstances, such as when it is necessary to obtain a virtually clean surface closely adjacent to one that is to be relatively thickly covered.

Accordingly, it is an object of the present invention to provide a novel method and apparatus for the production of a unified, adherent coating of a heat fusible resin upon a limited portion of a workpiece.

A more specific object of the invention is to provide such a method and apparatus for electrostatically coating the workpiece and for effecting the removal of the resinous material from selected portions thereof which are to be uncoated.

An even more specific object is to provide such a method and apparatus whereby a generally cylindrical article having reentrant surface portions may be coated with an adherent deposit upon the reentrant surface portions thereof. Another object of the invention is to provide such a method and apparatus whereby such coatings may be produced quickly, easily and economically, which method and apparatus may be automatic and continuous.

A further object is to provide a novel precuring device which is adapted to set the coating at one zone of a workpiece while simultaneously maintaining the particulate form of the resin at a second zone to facilitate its complete removal therefrom.

SUMMARY OF THE DISCLOSURE It has now been found that the foregoing and related objects of the invention are readily attained in an apparatus comprising, in combination, a chassis, means on the chassis for producing a cloud of electro-statically charged solid particles of resinous material, a precuring unit on the chassis, and means for carrying the work piece along a travel path through the cloud-producing means and precuring unit. The precuring unit includes means for heating a first zone of a workpiece to be coated, and means for simultaneously cooling a second zone thereof, the zones of the workpiece being in heat conductive contact with one another. The heating and cooling means are so disposed as to enable heating of the first zone of the workpiece to a relatively high temperature above ambient while the second zone thereof is simultaneously maintained at a relatively low temperature substantially below the relatively high temperature. Exposure of the workpiece to the charged particles from the cloud-producing means, with the workpiece charged effectively opposite to the particles, causes a layer of particles to deposit thereon. In the precuring unit, the .heating means at least partially fuses and coheres the particles at the first zone of the workpiece and the cooling means substantially prevents fusion and coherence of particles at the second zone thereof, removal of the particles from the second zone thereby being facilitated.

In preferred embodiments of the invention, the heating and cooling means of the precuring unit extend along substantially the same length of the travel path, and the cooling means comprises an element having a cooled support surface upon which the second zone of the workpiece rests in heat transfer contact during movement through the unit. The cooling means may additionally include an overlying element having a cooled lower surface extending substantially parallel to and in spaced alignment over the support surface to provide a convective cooling effect upon the second zone of the workpiece during passage therebeneath. ln such a case, the conveyor may include an upstanding element for supporting the article with the first and second zones of the article lying on opposite sides thereof, and the conveyor element may cooperate with the underlying element of the cooling means to provide a shield against heat flow by radiation and convection to the second zone of the article.

The apparatus preferably includes cleaning means positioned on the chassis along the travel path downstream of the precuring unit for effecting the removal of particles of resinous material from the second zone of the workpiece. Most desirably, it also includes post heating means positioned along the travel path downstream of the cleaning means. The post heating means is adapted to fully heat the workpiece so as to unify and produce from the remaining particles of resinous material an adherent coating on the first zone thereof.

The apparatus may be particularly adapted for producing a coating upon a generally cylindrical article having a central portion providing the first zone thereof and end portions extending axially from either side of the central portion together providing the second zone of the article. In such an instance, the cooling means of the precuring unit desirably comprises two elements, each having a cooled surface extending along an opposite side of the travel path and being adapted to support and cool one of the end portions of the article during movement thereof along the travel path through the unit. The heating means thereof may comprise a heating element extending along the travel path and lying generally between the cooled surfaces to heat the central portion of the article during movement through the unit.

The precuring unit may include a base providing at least in part the cooling means thereof. The base may have an elongated channel extending therein along the travel path through which at least the lower portion of the conveyor passes, the surfaces of the base defining the channel being cooled to provide a cooling effect thereabout. Preferably, the heating means employed comprises a heating element supported by a cover member which is movably mounted upon the chassis for displacement from a normal position over the travel path to a position outwardly therefrom. When the cooling means includes an overlying element having a cooled lower surface, such an element may be supported by the cover member and disposed as hereinbefore described when the cover member is in closed position.

In especially preferred embodiments of the invention the cloud producing means employed in the apparatus includes an electrostatic cloud chamber. Such a chamber may comprise a receptacle having means for producing a fluidized bed of charged particles including a gas-permeable plate extending thereacross in a generally horizontal intermediate plane and spaced above the bottom wall of the receptacle to define a plenum chamber therebelow. The receptacle also has electrode means extending thereacross to electrostatically charge particles of solid resinous material passing proximate thereto. Most desirably, the apparatus will include a particulate material reservoir having feed means communicating with the cloud chamber. In such a case, the electrode means may span a lesser area than the gaspermeable plate to provide an electrode-free vertical corridor within the receptacle through which particles of the resinous material may pass without acquiring a significant charge. A device for sensing the level of the bed of particles within the receptacle, in response to which the feed means conveys resinous material from the reservoir to the chamber when the bed level falls below a preselected height, may also be provided. The sensing device is positioned within the vertical corridor over the horizontal porous plate, to thereby minimize the effect of electrostatic charging upon the sensed level of the bed. The electrode employed may be a generally planar, grid-like structure disposed adjacent the upper surface of the gas-permeable plate, and electrode and plate may be substantially coextensive except at one area of the plate over which the electrode does not extend, thereby providing the electrode-free v'ertical corridor.

Certain objects of the invention may be attained by the provision of a precuring unit adapted for heating 'the cylindrical core portion of an electric motor armature rotor while simultaneously cooling the axially extending shaft portions thereof during passage through the unit. The unit comprises a base having an elongated, upwardly opening channel extending therein with generally horizontal upper surfaces of the base extending along each side of the channel, means being provided for cooling such surfaces to conductively cool shaft portions resting thereon. The channel is dimensioned and configured to receive the core portion of the rotor suspended therewithin with the shaft portions thereof resting upon the upper surfaces. The precuring unit also includes an elongated heating element which is normally axially aligned over the channel and is disposed to heat the core portion during passage through the channel.

Additional objects are attained in accordance with the method of the invention in which a unified, adherent coating of heat-fusible material is produced upon only a portion of a workpiece having proximate first and second zones in heat conductive contact with one another. The method involves producing a cloud of electrostatically charged solid particles of resinous material and exposing the workpiece to the charged particles with the work-piece charged effectively opposite thereto to cause a layer of the particles to deposit over the first and second zones thereof. The first zone of the work-piece is heated to a relatively high temperature above ambient while the second zone is simultaneously cooled. As a result, the particles on the first zone of the workpiece are at least partially fused and cohered while fusion and coherence of particles on the second zone are substantially prevented due to the relatively low temperature maintained thereat, which is substantially below the relatively high temperature of the first zone. Thereafter, particles of resinous material remaining on the second zone of the workpiece are removed.

Subsequent to the simultaneous heating and cooling step, the method will generally include the step of heating the workpiece to at least about the melting point of the resinous material to unify the particles thereof and to produce an adherent coating upon the first zone of the workpiece. In addition, it may include the step, effected prior to the simultaneous heating and cooling step, of removing a portion of the layer of particles deposited upon the first zone of the workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a plan view of apparatus embodying the present invention;

FIG. 2 is a side elevational view thereof;

FIG. 3 is a side elevational view of the coating process unit of the apparatus of FIGS. 1 and 2, drawn to 7 an enlarged scale and with housing portions removed structure provided at the load zone and showing an armature rotor carried on the forward conveyor for movement therethrough;

FIG. 7 is an end view of the electrostatic coating station along line 7-7 in FIG. 3 with portions of the housings broken away to illustrate the internal features thereof and drawn to a greatly enlarged scale;

FIG. 8 is a side elevational view of the sensing device employed in the cloud-coating unit of the electrostatic coating station;

FIG. 9 is a fragmentary end view along line 9-9 in FIG. 3 showing the powder removal zone of the apparatus with the contact belt unit thereof in its normal operating position, drawn to a greatly enlarged scale and having portions in vertical section to illustrate the construction thereof;

FIG. 10 is a front view of the powder removal zone at an acute angle to the upper surface of the deck, drawn to a slightly diminished scale from that of FIG. 9 and showing the contact belt unit in its raised position;

FIG. 11 is a fragmentary end view of the powder re moval zone along line 11-11 of FIG. 3, drawn to the scale of FIG. 9;

FIG. 12 is a fragmentary plan view of the shaft cleaning units provided within the powder removal zone, drawn to a scale enlarged from that of FIG. 10 and with the hold-down brackets removed to expose the vacuum slots thereof;

FIG. 13 is a side elevational view of the vacuum nozzle and associated parts employed with each of the units of FIG. 12;

FIG. 14 is an enlarged sectional view along line 14-14 in FIG. 3 showing the precuring unit of the apparatus with an armature rotor passing therethrough, and in phantom line showing the raised position of the cover assembly;

FIG. 15 is a perspective view of the air knife assembly at the powder recovery zone of FIG. 3, drawn to a greatly enlarged scale;

FIG. 16 is a fragmentary perspective view to a greatly enlarged scale of the intermediate conveyor employed in the apparatus; and

FIG. 17 is a fragmentary perspective view of one band of the endmost conveyor of the apparatus, drawn to the scale of FIG. 16.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENT Turning now in detail to the appended drawings, therein illustrated is an armature slot-coating system embodying the present invention and details of the various units and zones thereof. FIGS. 1 and 2 illustrate the overall layout of the system, the heart of which is the coating process unit, so designated on the drawing. Auxiliary to the coating process unit is an oven and a cooling unit, and main control and oven control facilities are furnished. Also included in the system to enable a desirable mode of operation is a power recovery and feed unit and a powder replenishment unit. As will be appreciated from FIG. 2, the workpieces are loaded in an infeed zone at the left-hand end of the coating process unit from which they pass serially through an electrostatic coating zone, a powder removal zone, a precure zone, and a powder recovery zone; they then pass into the oven and finally through the cooling unit. Excess powder from the electrostatic coating zone is recovered in the powder recovery and feed unit and is returned through an appropriate conduit to the coating unit on a substantially continuous basis, and additional powder is furnished from the powder replenishing unit as needed. An electric interface access channel runs along the rear of the coating process unitv to provide power at the various zones thereof.

With specific reference now to FIG. 3, the coating process unit of the system is depicted in greater detail. It includes a frame 10 on which are rotatably supported three conveyor drive sprockets, generally designated by the numerals ll, 12 and 13 respectively from left to right in the Figure, and idler wheels 14 are positioned between adjacent sprockets. A forward endless conveyor, generally designated by the numeral 16, runs about sprockets l1 and 12 and the idler wheel 14 therebetween; a center endless conveyor, which is generally designated 18, runs about sprockets l2 and 13 and about the idler wheel 14 positioned between them, and a rearward endless conveyor, which is generally designated 20 and is fragmentarily illustrated, runs about the right-hand sprocket 13 and a cooperating sprocket which is not illustrated and is positioned adjacent the end of the cooling unit shown in FIGS. 1 and 2. A drive pulley 22 operates the powder removal unit and is driven by the electric motor 24 which is supported within the frame 10. A second motor 25 is connected to sprocket 13, thereby synchronously driving all con veyors 16, 18, 20 since they are coupled by the sprockets, 11, 12, 13. 7

Although the invention is not to be construed as lim ited to coating of any particular workpiece, and may be feasible for coating selected portions of objects which are elongated or of continuous length, the system illustrated is especially suited for the coating of armature rotors of the type generally designated by the numeral 26 in FIG. 4, and is intended principally for that purpose. The rotor 26 is of conventional configuration and includes a cylindrical core portion 28 having spaced about its circumference four axially extending, reentrant winding slots 30. Extending from opposite ends of the core portion 28 are simple and crank-type shafts 32, 34 respectively, and the shaft 34 has a spring clip 35 engaged upon it adjacent the end of the core portion As will be appreciated, the slots 30 of the rotor 26 are designed to receive wire windings, making it necessary to provide the slots 30 and the opposite end faces 37 of the core portion 28 with a layer of insulating material to enable magnetic poles to be defined thereon. It is also important that the outer circumferential surface of the core portion 28 and the shafts 32, 34 be free from insulating material; the present system is unique in enabling the rapid and facile production of coated rotors having deposits of insulating material which are present only at selected locations and are of substantially uniform thickness.

FIG. 5 illustrates in greater detail the loading zone of the coating process unit, whereat a narrow rectangular opening 38 is provided through the deck 36 of the frame 10 to accommodate the edge of drive sprocket 11. As can be seen, the forward conveyor 16 is comprised of two independent flexible and continuous parallel bands, generally designated by the numerals 44 and 45, and the drive sprocket 11 consists of a pair of parallel sprocket wheels 40 mounted on a common shaft for concurrent rotation. Each of the sprocket wheels 40 has about its circumferential edge a multiplicity of small rectangular teeth 42; the belt portion 46' rectangular teeth 42 of the respective sprocket wheels 40 as the bands pass thereover along their travel path. Extending at a right angle from the inner edge of the belt portion 46 of each of the bands 44, 45 are a multiplicity of carrier tabs 50, 50 respectively, and each tab 50, 50' has bevelled shoulders 51 leading into the shaft slots 52, 52' therebetween. As will be appreciated, the slots 52, 52' are dimensioned to receive the shafts of the armature rotor 26, and the tabs 50' are slightly narrower than the tabs 50 to render the slots 52' somewhat wider than the slots 52, thereby enabling close-fitting engagement of shafts 32, 34, notwithstanding their different diameters. It will be evident that the bevelled shoulders 51 facilitate insertion and removal of the shafts of the armature rotors 26 into and from the slots 52.

As can most readily be seen by additional reference to FIG. 6, one of a pair of elongated rectangular curb blocks 54 extends along each side of the upper flight of the conveyor 16, with the curb blocks 54 being secured to the deck 36 by bolts 56 (fastened in an appropriate manner, not illustrated). Coextensive with each of the curb blocks 54 is a guide rail 58 which is secured upon the upper surface of the associated curb block 54 by a number of-bolts 60 spaced along the length thereof. A shallow recess 61 is provided along the upper surface adjacent the inner edge of each of the curb blocks 54 enabling the belt portion 46 of the conveyor bands 44, 45 to'pass between the curb blocks 54 and the bottom surface of the guide rails 58. The guide rails 58 have inner surfaces which extend downwardly and then at an angle inwardly to provide guide surfaces 62 sloping downwardly toward the travel path. The guide surfaces 62 define therebetween a trough which is dimensioned so that armature rotors 26 carried by the conveyor 16 extend there-across with little free space adjacent the ends, thus ensuring that the rotors 26 remain accurately positioned across the conveyor 16 and centrally positioned on the axis of the travel path of the unit.

Extending forwardly from adjacent the ends of the curb blocks 54 is a support extension 64 which underlies the conveyor 16 and provides support therefor as thebands 44, 45 disengage from the sprocket wheels 40. Supported above the extension 64 is a loading platform portion 66 from which extend rearwardly a pair of thin support rails 68 which are secured in a parallel relationship against the inner faces of the curb blocks 54. The loading platform 66 is provided to facilitate loading and seating of the rotors 26 in the slots 52 of the conveyor 16, and the support rails 68 provide underlying support for the shafts 32, 34 as the rotors 26 proceed along the travel path, it being appreciated that the shafts ride upon the upper edges of the support rails 68 rather than resting at the bottom of the slots 52. As a result, the conveyor 16 serves only to drive the rotors 26 forwardly through thesystem, with contact upon the rails 68 causing them to rotate as they are conveyed. From the load zone, the armature rotors 26 are conveyed to the electrostatic coating station illustrated in detail in FIG. 7, which is comprised of a hood, a powder feed stack, and an electrostatic coating chamber, generally designated by the numerals 72, 74 and 76 re 8 spectively. The electrostatic coating chamber 76 consists of an upwardly opening enclosure 78 secured against the bottom surface of the deck 36 and having a bottom wall opening through which air is charged from a pressurized source 79 thereof. A horizontal porous ceramic partition 80 divides the enclosure 78 into a lower air plenum chamber 82 and an upper cloud chamber 84. The partition 80 supports an overlying grid-type electrode 86 connected to a diagrammatically illustrated high voltage source 88 and extending partially across the enclosure 78 to provide an electrodefree area 85 between its inner edge 87 and the sidewall 89, through which extends an imaginary vertical corridor.

Within the corridor, supported upon the depending bracket 92, is a pneumatically operated fluidic sensing device comprised (asseen in FIG. 8) of a body 90 with a wire actuating finger 94 extending therefrom; one appropriate device is sold by Norgren Fluidics of Littleton, Colorado under the name FEATHERFLEX 5FS- 010-000. On the outer end of the wire finger 94 is a float sphere 96 which may be fabricated of a foamed polystyrene or comparable lightweight material, and pneumatic control lines 98 extend from the body 90 and are connected to control means (not illustrated). The feed stack 74. consists of a-sifter box 100 having a screen 102 horizontally positioned across the central portion thereof and having a recycle feed conduit 104 a and a replenish conduit 106 leading thereinto. As will be appreciated, the conduit 104 extends from the powder recovery and feed unit and the conduit 106 extends from the powder replenishment unit, both shown in FIGS. 1 and 2. The conduits 104, 106 deliver thermoplastic resin powder 103 into the upper portion of the sifter box from which it passes through the screen 102 and the opening 108 in the deck 36 with lumps and foreign matter being removed by the screen 102. The powder 103 then falls upon the porous partition 80 where it becomes fluidized by air passing upwardly from the plenum chamber 82 in a conventional manner. The fluidized powder 103 exerts an upward force upon the float sphere 96 of the fluidic sensing device; when the quantity of powder 103 above the partition 80 is insufficient to urge the sphere 96 (and hence the actuating finger 94) upwardly to the necessary extent, a signal from the sensor causes the control means (not illustrated) to deliver an additional quantity of powder 103 through the conduit 106 from the powder replenish unit, thereby correcting the deficiency.

The hood 72 is positioned over an elongated slot 110 in the deck 36 along which the parallel guide rails 68 extend. It is secured to the deck by bolts 112 and has a tunnel portion 114 with an end wall 116 forming a partial closure therefor and defining a tunnel opening at each end thereof. A stack portion 118 extends upwardly from the tunnel portion 114 of the hood 72, and has a takeoff conduit 120 which is attached to a suitable vacuum source and enables excess powder to be removed from the coating station. Such powder is returned to the recovery and feed unit for ultimate recycle through the conduit 104 leading to the feed stack 74. An elongated baffle plate 122 is inclined downwardly from each sidewall of the tunnel portion 114 toward the travel path of the unit, and the plates 122 cooperate with the carrier tabs 50, 50' to confine powder 103 which passes upwardly through the slot 110 to the central portion of the rotors 26 passing thereover.

As will be appreciated, the powder 103 employed for the coating operation is of such a nature that it is capable of acquiring an electrostatic charge as the particles pass through the grid electrode 86. The rotors 26 are maintained at ground potential (such as by grounding the conveyor 17 with which they are in contact) during passage over the slot 110, thus causing attraction and adherence of charged powder particles to the surfaces of the rotors 26, with the electrostatic effect ensuring that all exposed surfaces, including winding slots 30, are coated. Due to the charge on the powder particles, it is important that the fluidic sensing device be positioned over the electrode-free area 85 of the horizontal partition 80. In this region charging of particles is minimized, as a result of which the attractive force from the grounded rotors 26 is quite insignificant and particles thereat are elevated only by the buoyant effect of the pressurized air. Otherwise, the electrostatic force on the particles would lead to an inaccurate indication of the quantity of powder present in the system, rendering control of the automatic replenishment system virtually ineffective.

Since the armature rotors 26 must be substantially free of insulating material on the circumferential surface of the core portion 28 and along the shafts 32, 34, and since in the coating step powder deposits upon all exposed surfaces, the method and apparatus of the invention require that means be provided for removing powder from selected surfaces of the rotor 26 where it is unwanted. To that end, the illustrated apparatus is provided with a powder removal station which includes the contact belt unit, generally designated by the numeral 124, and shown, in FIGS. 3, 9 and 10. The contact belt unit 124 includes an elongated forward frame member 126 from which extend rearwardly triangular mounting brackets 128 which are pivotally supported upon posts 130 projecting upwardly from the deck 36. In this manner, the unit 124 is hingedly supported for ready displacement from the position over the deck 36 shown in FIG. 9 to its open position in FIG. 10. Affixed in a central location behind the forward frame member 126 is a pinion block 131 which, in turn, has a gear train block 132 mounted behind it. A short central shaft 134 is journaled at its ends by appropriate means to extend transversely through the forward frame member 126, the pinion block 131, and the gear train block 132, and it has a drive gear 136 affixed on it within the gear train block 132. The shaft 134 also has a drive pinion 138 affixed to it in front of the gear 136, with the pinion 138 residing generally within the pinion block 131. A lower shaft 140 is journaled at its ends and extends transversely between the pinion block 131 and the gear train block 132; on it is affixed, in meshing engagement with the drive gear 136, an upper transfer gear 142. The transfer gear 142 communicates through a deck opening 143 with a lower transfer gear 144 which is supported upon a shaft 146 positioned and appropriately journaled (by means not shown) below the deck 36. As can be seen in FIG. 3, the lower transfer gear 144 meshingly engages a gear 148 which is affixed to the shaft on which the drive pulley 22 is supported. In this manner, power is delivered from the motor 24 through the drive pulley 22 and the train of gears 148, 144, 142 ultimately to the drive gear 136 for the contact belt unit 124. As can be seen, pivoting the unit 124 upwardly about the posts 130 simply disengages the gears 142 and 144, discontinuing operation of the unit 124 and permitting access to the normally covered portion thereunder.

A belt pulley shaft 150 is journaled in the forward frame member 126 and pinion block 131 on either side of the central shaft 134, and a pulley pinion (not exposed but identical to pulley pinions 152 to be discussed hereinafter) is affixed to the inner end of each of the shafts 150 and is in meshing engagement with the drive pinion 138. (It will be understood that the pulley pinion on shaft 150 to the left of shaft 134 in FIG. 10 lies behind pinion 138, as viewed in FIG. 9, and that the pulleys and belt assembly at the left side of FIG. 9 are shown along a section line somewhat forward of line 9-9.) To the opposite ends of the pulley shafts 150 are affixed belt pulleys 154. Spaced to either side of the central pinion block 131 is an auxiliary pinion block 156 in which is contained a pair of belt pulley shafts 150 and a transfer pinion shaft 134 therebetween. The inner ends of the pulley shafts 150 have affixed to them pulley pinions 152 (as can be seen in the left-hand auxiliary pinion block 156 in FIG. 10) and the transfer pinion shaft 134 has affixed to its inner end a transfer pinion 158 in meshing engagement with each of the pulley pinions 152 on either side thereof. Adjacent each end of the forward frame member 126 is a rectangular bearing block 162 in which is journaled, by appropriate means, a belt pulley shaft 150. A belt pulley 154 of the type previously referred to is secured on the outer end of each belt pulley shaft supported in either the auxiliary pinion blocks 156 or the bearing blocks 162.

The eight pulleys 154 function as four sets with adjacent pairs 'of pulleys supporting a belt assembly consisting of an underlying support element 164 and an outwardly exposed contact element 166. The contact element is of foamed polyurethene or a comparable mate rial providing a cellular outer surface. Such a structure enables the contact element 166 to pick up powder from the surface of the core portion 28 simply by. contact therewith, with no wiping or brushing action being necessary or desirable. The support element 164 may be a timing belt (i.e., having transversely extending ridges about its inner surface) with the pulleys 154 being provided with corresponding ridges and grooves, or square teeth, to cooperate therewith. Drive power is transferred from the motor 24, through the gears 148, 144, I42, 136, to the pinion 138 within the central pinion block 131, and to the innermost belt pulleys 154. Due to the interconnection through the pulley pinions 152 and transfer pinion 158 within each of the auxiliary pinion blocks 156, the belt assemblies on the outer sets of pulleys 154 are simultaneously driven, with all belt assemblies rotating at precisely the same rate and in the same direction.

As is seen in FIG. 9, a central sprocket wheel 40' having rectangular circumferential teeth 42 is supported on a common shaft (not shown) with two outside sprocket wheels 40. The outside wheels 40 correspond to the sprocket wheels bearing the same numeral which constitute drive sprocket 11, and the three commonly supported wheels 40, 40' provide the intermediate drive sprocket 12. Endless conveyor 18 has the construction illustrated in FIG. 16 and passes about the central sprocket wheel 40'. The conveyor 18 consists of a central band 176 having carrier tabs 178, 178' extending at right angles from the side margins thereof. The tabs 178' are slightly narrower than the tabs 178, again to render the slots 180"there-betwcen slightly wider than the slots 180 between the tabs 178 to snugly receive the shafts 34, 32 of the rotor 26, respectively. The following edges of each of the tabs 178, 178' have bevelled shoulders 51 to facilitate entry of the shafts 32, 34 thereinto; however, it will be noted that the forward edges of the tabs 178, 178' are not bevelled, and the reason therefor will be explained directly.

As can be seen in FIG. a transfer of the rotors 26 occurs within the powder removal zone with the rotors 26 shifting from the forward conveyor 16 to the intermediate conveyor 18. Engagement of both conveyors 16, 18 on different sprocket wheels 40, 40 of the common drive sprocket l2 and the construction employed permits conveyor 18 to pass between the bands 44, 45 of the conveyor 16. At the point of common tangency of the conveyors l6, 18 to sprocket 12 the respective slots 52, 180 thereof are substantially aligned, causing the shafts 32, 34 of the rotors 26 to momentarilyreside in slots of both conveyors simultaneously. As the bands 44, 45 of the forward conveyor 16 pass downwardly about the sprocket 12, the upper corners of the tabs 180, 180 of the intermediate conveyor 18 engage behind the shafts 32, 34 to smoothly and effectively carry them out of the slots 52 with the bevelled shoulders 51 at the following edges of the tabs 50, 50 facilitating withdrawal. Thereafter, the rotors 26 are propelled through the system by the center conveyor 18.

Assuming movement to be in a left to right direction, contact of the ends of the shafts 32, 34 upon the support rails 68 causes rotation of the rotors 26 in a clockwise direction. If the motor 25 also drives the belt assemblies of the contact belt unit 124 in a clockwise direction, the direction of rotationof the rotors 26 will reverse upon encountering the lower flight of element 166 at the entrance of the unit 124 (the relationship at contact being as depicted in FIG. 9). Such contact causes a significant proportion of the powder on the outer circumferential surface of the cylindrical core portion 28 of the rotors 26 to be displaced therefrom and to fall into the powder recovery hopper 184, which is positioned at an appropriate location beneath the deck 36 (as may be seen in FIG. 3). The hopper 184 is connected to the powder recovery and feed unit through a vacuum system (not illustrated) by a conduit 186. Most of the remaining powder on the surface of the core portion 28 is picked up by the contact element 166 of the belt assembly, as previously described, with any additional powder being removed by the successive belt cleaning effects in the same manner. As will be appreciated, since the rotors 26 are supported for free rotation, after contact with the contact element 166 they turn at precisely the same speed under the influence thereof. This prevents relative wiping or brushing action between the element 166 and the rotors 26, such as would tend to cause uneven deposits to be produced at the edges of the slots 30. The nozzles 170 and associated vacuum conduits 172 are adjustably supported in the bifurcated end portions of the nozzle support arms 168 with the nozzles 170 lying closely adjacent the contact elements 166. In this way, the powder picked up by the elements 166 is withdrawn from the cells thereof and is conveyed to the recovery portions of the system for recycle.

Positioned within the powder removal zone near the forward end of the second belt assembly of the unit 124 is a pair of vacuum blocks 188, which are secured to the deck 36 along the sides of the travel path. As can best be seen in FIG. 12, each of these blocks has a face plate, 190,190 secured upon its uppersurface and of an elongated vacuum channel'l92extending lengthwise therein. As can be seen with additional reference to FIGS.',3 and 13, a vacuum nozzle 194 of generally oval cross section is secured against the lower surface ofeach of the vacuum blocks 188, each nozzle 194 having a circular throat portion 196 about'which is positioned an annular mounting collar 200 by which it is secured against the associated vacuum block 188 (by means not shown). Secured over the throat portion 196 of each nozzle 194 is a vacuum hose 198 which is connected to a vacuum source (not shown) and ultimately to the powder recovery and feed unit illustrated in FIGS. 1 and 2.

The face plates 190, 190' on the vacuum blocks 188 are provided with elongated slots202, 202', each of which extends in a generally angular relationship outwardly from the travel path. These slots 202, 202' register overthe channels 192 in the blocks 188 and serve to define a flow passage for air under the influence of vacuum drawn through the conduits 198. As the armature rotors 26 travel between the vacuum blocks 188 with the shafts 32, 34 thereof in rolling contact upon the face plates 190, 190' respectively, the vacuum effect from below thoroughly'cleans the shafts 32, 34 of any powder which may have become deposited thereon. Normally, powder will be present in the shafts 32, 34 as a result of the initial electrostatic coating operation and/or due to displacement from the circumference of the cylindrical core portion 28 during powder removal by the first belt assembly in the contact belt unit 124. The divergent disposition of the slots 202, 202' will cause particles of powder to be removed first from the portions of the shafts 32, 34 adjacent the core portion 28 and progressively outwardly therealong. It will be appreciated that the nonlinear and nonuniform configuration of the slot 202' is' necessitated by the configuration of the crank shaft 34 which passes thereover. As can be seen in FIGS. 9 and 10, a hold-down bracket 201 is secured to each of the vacuum blocks 188. Each bracket 201 includes a pressure plate element 203 which overlies the slot 202, 202' of the associated block 188 and serves to engage the tops of the shafts 32, 34 as they areconveyed thereunder, thereby forcing the shafts against the face plates 190, 190' to ensure efficient powder removal therefrom.

After travelling past the vacuum blocks 188, the armature cores 26 are conveyed beneath the third of the series of belt-cleaning assemblies while being supported upon parallel side rails 182. The fourth contact belt effect is similar in design to the first three, with the exception that it is provided with contact belt assemblies for the shafts 32, 34 as well as for the cylindrical core portion 28 of the rotors 26. The construction of this portion of the contact belt unit 124 is most clearly illustrated in FIG. 11, wherein it can be seen that a set of three belt pulleys 154 are 'mounted on a common shaft for simultaneous rotation. Each of the pulleys has a belt assembly consisting of a support belt 164 and a contact belt 166 constructed as hereinbefore described, and it will be appreciated that the belts extend between two of such sets of three belt pulleys 154 (as can be seen in FIG. 10).

From the contact belt unit 124, the armature rotors 26 pass into a precuring unit, generally designated by the numeral 204 and shown in FIGS. 3 and 14. With specific reference to the latter figure, it can be seen that the precuring unit 204 consists of a cover assembly, generally designated by the numeral 206, which has affixed thereto a pair of angle brackets 208, only one of which is visible in FIG. 14. The brackets 208 are secured at one end to the cover assembly 206 by appropriate bolts 210, and the opposite ends thereof are pivotally supported upon posts 212 which are mounted upon the deck 36 of the machine. Also secured to the cover assembly 206 is a right angle contact arm 214 which has an element extending over the end of a spring'loaded plunger assembly 216. In normal operation the cover assembly 206 will be maintained in the position illustrated in full line in FIG. 14 by fluid pressure means acting against the upward force of the plunger assembly 216. If the machine stops or if some emergency situation occurs, the fluid pressure force is disrupted, permitting the plunger assembly 216 to immediately raise the cover assembly 206 to the position shown in phantom line.

The cover 218 of the cover assembly 206 is elongated (as can be seen in FIG. 3) and is of inverted, generally Ushaped configuration (as is shown in FIG. 14). It has a number of layers 220 of insulating material lining the top wall thereof, which are secured, along with a metal sheet reflector 222 and a pair of elongated angular baffle plates 224, to the cover 218 by appropriate bolts 226. Heating elements 228, which may be CALROD units, extend longitudinally within the cover 218 and are supported therein by a number of inserts 230, which are spaced along the length of the cover 218 and have pairs of apertures 231 to receive and support the heating elements 228. The baffle plates 224 are constructed with inclined walls 232 which slope downwardly and inwardly toward one another and toward the travel path; the walls serve to support the inserts 230 as well as their primary function of reflecting and concentrating heat from the elements 228 upon the central portion of the travel path.

Supported along each side of the cover 218 at the lower edges thereof is one of a pair of configured cooling blocks 234, which may be constructed of aluminum or another suitable material having a high heat transfer coefficient. It will be appreciated that these cooling blocks are elongated and extend along substantially the entire length of the cover 218. The cooling blocks 234 have inner upstanding elements 235 which are configured to define behind them circular recesses 236, in which are supported cooling tube portions 238. Small, downwardly opening U-shaped channels 240 are defined along the lower inner edges of the upstanding elements 235, and a depending ridge 242 is provided on each of the cooling blocks 234 adjacent the lower outer edge thereof.

The ridges 242 of the cooling blocks 234 are received in narrow, upwardly opening U-shaped channels 244 defined in the upper surface of the base of the precuring unit 204, the base being generally designated by the numeral 246. A relatively large, upwardly opening U shaped channel 250 extends axially in the base 246 along its entire length to define the travel path therethrough. The underside of the base 246 has a U-shaped channel 248 of a similar size running along its length, with the opposed relationship of the channels creating a relatively thin floor portion 252 therebetween. A rectangular base block 254 is seated in the downwardly opening channel 248 and is welded in place with its upper surface spaced a short distance downwardly from the lower surface of the floor portion 252 to define a shallow water channel 256 therebetween. Upwardly opening U-shaped slots 258 are formed in the upper surface of the block and along the entire length thereof between the central channel 250 and each of the relatively narrow channels 244, and each of the slots 258 has a cover strip 260 engaged over its open end to thereby define closed conduits therewithin.

At each end (only one end being shown) the base 246 is provided with a transverse bore 262 which communicates with the opposite ends of the shallow water channel 256. To facilitate manufacture, the bores 262 are simply drilled inwardly from the side of the base 246, with plugs 264 being inserted afterward to close the ends. Extending upwardly and inwardly from the opposite ends of the bores 262 are short connecting channels 266 (only two of the four of which are seen because only one end of the base 246 is illustrated), one of which communicates with each of the U-shaped slots 258 at one end thereof. Finally, an inlet port 268 communicates from the lower surface of the base 246 with the transverse bore 262, and it will be appreciated that the other end of the base 246 has a similar port 268 communicating with the associated bore 262 provided thereat.

In operation, the precure unit 204 heats the cylindrical core portion 28 of each of the armature rotors 26 while simultaneously cooling the shafts 32, 34 thereof. Heat is generated by the elements 228, with the reflector 222 and the baffle plates 224 effectively directing the heat inwardly toward the core portion 28 and concentrating it thereat. The simultaneous cooling effect is provided by passing water through the base 246 and the configured cooling blocks 234. With respect to the base 246, water passes inwardly through illustrated port 268, transversely across the block in the bore 262, and thence along the length of the base 246 within the shallow water channel 256 and the U-shaped slots 258 to pass outwardly through the transverse bore and port not illustrated. In this manner, a cooling effect is transmitted through the thin floor portion 252 to cool the central band 176 of the conveyor 18 and the surrounding area. Water passing through the slots 258 serves not only to cool the sides of the conveyor 18, but has the primary function of producing a cooling effect through the cover strips 260. The shafts 32, 34 of the armature rotors 26 contact these strips 260 directly, so that the cooling water passing therebeneath very effectively lowers the temperature of those portions. The configured blocks 234 are cooled by water passing into one of the cooling tube portions 23 and out of the other, the portions 238 being parts of a continuous conduit. As a result, the horizontal part 237 of each of the blocks 234 is cooled and cooperates with the base 246 to effectively maintain the shafts 32, 34 at a relatively low temperature. The upper ends of the carrier tabs 178, 178 of the conveyor 18 extend into the downwardly opening U-shaped channels 240 adjacent the lower inner edges of the blocks 234, and are cooled thereby. In addition. the engagement of the depending ridges 242 in the upwardly opening channels 244 increases the effectiveness of cooling by unifying the cover 218 and base 246 of the precure unit 204. A low temperature shell is thereby defined about the travel path through the precuring unit 204, except in the limited area thereabove at which the heating effect is concentrated. Ac-

cordingly, the unit 204 very effectively cools parts of the rotors 26 which lie outwardly of the cylindrical core portion 28, while the portion 28 is heated to a relatively elevated temperature. As a result, only resin on the core portion 28 is melted and fused, with any powder remaining on the shafts 32, 34 being maintained in a solid particulate state. This permits removal of unwanted powder from the shafts 32, 34 while simultaneously producing a relatively adherent coating in the slots 30 of the core portion 28, the circumferential surface of the core portion 28 having been freed from powder by the action of the belt assemblies in the contact belt unit 124.

Turning now in detail to FIG. 15, therein illustrated is an air knife assembly, generally designated by the numeral 270, which is positioned immediately downstream from the precure unit 204, as can be seen in FIG. 3. The air knife assembly 270 consists of a pair of spaced, inverted U-shape bridge members 272 which have mounted thereon a pair of spaced air manifold bars 274. The manifold bars 274 are adjustable (by means not shown) to vary their spacing and angular attitude relative to one another, and each of them has a number of flattened nozzles or air knives 276 extending downwardly therefrom toward the deck 36 of the machine. In general alignment under each of the manifold bars 274 is an upwardly opening elongated trough 278 which is connected to a vacuum source (not shown) through vacuum conduits 280 attached to the lower ends thereof. As will be readily appreciated, armature rotors 26 pass from the precuring unit 204 beneath the bridge members 272 of the air knife assembly 270 with their shafts 32, 34 extending outwardly over the troughs 278. Air is charged under pressure into the manifold bars 274 through the air conduits 282 and is blown at high velocity upon the shafts 32, 34 through the air knives 276 as the rotors 26 travel through the assembly 270. Due to the discrete form in which the particles are maintained as a result from the cooling effects of the precuring unit 204, the air from the knives 276 effectively dislodges any particles present on the shafts 32, 34 and propels them into the troughs 278. In this manner, the shafts are thoroughly cleaned prior to entry of the rotor 26 into the oven, with the excess powder being returned to the system through the conduits 280.

Uncoated armature rotors 26 are loaded in successive pairs of slots 52, 52 of the conveyor bands 44, 45 at the infeed station of the apparatus, and enter the oven with at least partially fused and cohered coatings of resin in the slots 30 and on the end faces 37 thereof. The circumferential surfaces of the cylindrical core portions 28 of the rotors 26 are virtually devoid of any powder particles. This is accomplished by the contact belt elements 166, which effectively remove all powder deposited thereon without causing significant amounts of the resin to be removed or built up at the edges of the slots 30, which is achieved due to the absence of any wiping effect.

The shafts 32, 34 are preliminarily cleaned in the belt contact unit 124 by passage over the slotted face plates 190, 190 'of the vacuum blocks 188, and by the contact elements 166 of the fourth set of belt assemblies, as illustrated in FIG. 11. However, it should be appreciated that either or both of these effects might be eliminated, with reliance being placed entirely upon the action in the precuring unit 204 to permit powder removal, but

preferably both the contact belt unit 124 and also the precuringunit 204 will be provided as illustrated. From the precuring unit 204fthe rotors 26 are carried to. the air knife assembly 270 for a final cleaning, through the oven for complete fusion, and finally to the cooling unit for solidification of the resin.

Subsequent to the air knife assembly 270 and ahead of the oven is a second transfer'point which occurs over the rearmost drive sprocket 13, Since the transfer is quite comparable to that which occurs over the sprocket 12, a detailed explanation is not believed to be necessary. However, as illustrated in FIG; 16, the construction of the conveyor 20 to which the cores are transferred at this point is somewhat different from any described previously. More particularly, the conveyor 20 consists of a pair of spaced chain assemblies, gener ally described by the numeral 283 (only one being shown in FIG. 16) which, at the point of transfer, lie to either side of the conveyor 18. Each of the chain assemblies 283 includes an endless sprocket chain 292 on which is mounted a multiplicity of U-shaped cradles 284. Each of the cradles 284 has in its inner wall 288 an upwardly opening U shaped socket 286 in which the shafts of the rotors are received. The cradles 284 have a depending flange element 290 secured thereto, and the flange elements constitute part of the sprocket chain 292 while affording the means of attachment thereto. As will also be appreciated, drive sprocket 13 will consist of a pair of sprocket wheels similar to those employed for the drive sprocket 12, one wheel being used to support and drive each of the chain assemblies 283.

The particular fusible resin used may vary greatly; however, of the types of materials which are suitable, thermoplastics, and particularly. synthetic thermoplastic resins, are preferred. Exemplary of such thermoplastic resins are the vinylidenes and vinyls (e.g., polystyrene and polyvinyl chloride), the olefins (e.g., polyethylene, polypropylene and copolymers thereof), the cellulosics, polyamides (e.g., nylons), etc.

As will be appreciated by those skilled in the art, many changes may be made in the illustrated apparatus without departing from the concept of the invention hereof. For example, heating may be by any appropriate means, and may employ convection, conduction, infrared, induction, or like effects. Similarly, cooling may be accomplished in any appropriate manner, such as by the use of cooled air or other fluid, conventional refrigeration, etc. The proper electrical circuitry will also be readily apparent and of the typeconventionally employed in the electrostatic coating and electromechanical arts. It should be appreciated that, although good practice and safe operating procedures will normally dictate electrical grounding of the apparatus and of the workpiece by contact therewith, no special provision need normally be made for grounding of the workpiece to ensure adequate electrostatic attraction and adhesion. The high voltage charging of the particles will usually suffice to establish an adequate potential relative to the workpiece, regardless of the measures taken with respect to the latter; however, independent connections may be made to the workpiece if so desired.

As used herein, the terms partial fusion" and coherence are intended to connote a state in which the individual particles of the resin have been affected by heat sufficiently to at least loosely join them together,

so as to resist separation. in such a condition individual particles may be discernible, whereas upon complete fusion or melting the particles are no longer identifiable as such. Due to the variety of resinous materials that may be employed in the practice of the invention, it is not possible to place specific values upon the temperatures involved for fusion or melting without unduly limiting the scope thereof. Moreover, the conditions of operation that are appropriate in each instance will be readily apparent to those skilled in the art in view of the foregoing detailed information.

Thus it can be seen that the present invention provides a novel method and apparatus for the production of a unified, adherent coating of a heat fusible resin upon a limited portion of a workpiece. More specifically, it provides such a method and apparatus for electrostatically coating the workpiece and for effecting the removal of the resinous material from selected portions thereof which are to be uncoated, and the method and apparatus are particularly adapted for coating reentrant surface portions of generally cylindrical articles. The coatings are produced quickly, easily and economically, and on an automatic and continuous basis if so desired. A novel precuring device is also provided which is adapted to set the coating at one zone of a workpiece while simultaneously maintaining the particulate form of the resin at a second zone to facilitate its complete removal therefrom.

Having thus described the invention we claim:

1. A method for the production ofa unified, adherent coating of heat-fusible material upon only a portion of a workpiece having proximate first and second zones in heatconductive contact with one another, comprising the steps of:

a. producing a cloud of clectrostatically charged solid particles of heat-fusible resinous material;

b. exposing said workpiece to said charged particles with said workpiece charged effectively opposite thereto to cause a layer of said particles to deposit upon said first and second zones thereof;

c. heating said first zone of said workpiece to a relatively high temperature above ambient while simultaneously cooling said second zone thereof to cause at least partial fusion and coherence of said particles on said first zone while maintaining said second zone at a relatively low temperature sub stantially below said relatively high temperature to substantially prevent fusion and coherence of particles on said second zone to thereby facilitate removal therefrom;

d. thereafter removing from said second zone any of said particles of resinous material remaining thereon,

said simultaneous heating and cooling step producing a relatively steep temperature gradient between said first and second zones, so that the margins of said layer of particles on said first zone are relatively sharply defined.

2. The method of claim 1 additionally including the step of heating said workpiece subsequent to said simultaneous heating and cooling step to at least about the melting point of said resinous material to melt said particles thereof and to produce a unified and adherent coating upon said first zone of said workpiece.

3. The method of claim 1 additionally including the step of removing a portion of said layer of particles de posited upon said first zone of said workpiece prior to said simultaneous heating and cooling step.

4. The method of claim 1 additionally including the step of removing said layer of particles deposited upon said second zone of said workpiece prior to said simultaneous heating and cooling step.

5. The method of claim 1 wherein said resinous material is a synthetic thermoplastic resin.

6. The method of claim 1 wherein said workpiece is an armature rotor having a cylindrical core portion with axially extending slots about the circumference thereof, the surfaces of said slots comprising said first zone of said workpiece.

7. A method for the production of a unified, adherent coating of heat-fusible material upon only a portion of a work-piece having proximate first and second zones in heat-conductive contact with one another, comprising the steps of:

a. producing a cloud of electrostatically charged solid particles of heat-fusible resinous material;

b. exposing said workpiece to said charged particles with said workpiece at about ambient temperature and charged effectively opposite to said particles to cause a layer thereof to deposit upon said first and second zones of said workpiece;

c. thereafter heating said first zone of said workpiece to a relatively high temperature above ambient while simultaneously cooling said second zone thereof to cause at least partial fusion and coherence of said particles on said first zone while maintaining said second zone at a relatively low temperature substantially below said relatively high .temperature to substantially prevent fusion and coherence of particles on said second zone to thereby facilitate removal therefrom; and

d. thereafter removing from said second zone any of said particles of resinous material remaining thereon,

said simultaneous heating and cooling step producing a relatively steep temperature gradient between said first and second zones, so that the margins of said layer of particles on said first zone are relatively sharply defined, said step (d) being effected immediately after said step (c).

8. The method of claim 7 additionally including the step of heating said workpiece subsequent to said simultaneous heating and cooling step to at least about the melting point of said resinous material to melt said particles thereof and to produce a unified and adherent coating upon said first zone of said workpiece.

9. The method of claim 7 additionally including the step of removing a portion of said layer of particles deposited upon said first zone of said workpiece prior to said simultaneous heating and cooling step.

10. The method of claim 7 additionally including the step of removing said layer of particles deposited upon said second zone of said workpiece prior to said simultaneous heating and cooling step.

11. The method of claim 7 wherein said resinous material is a synthetic thermoplastic resin.

12. The method of claim 7 wherein said workpiece is an armature rotor having a cylindrical core portion with axially extending slots about the circumference thereof, the surfaces of said slots comprising said first zone of said workpiece. 

1. A METHOD FOR THE PRODUCTION OF A UNIFIED, ADHERENT COATING OF HEAT-FUSIBLE MATERIAL UPON ONLY A PORTION OF A WORKPIECE HAVING PROXIMATE FIRST AND SECOND ZONES IN HEAT-CONDUCTIVE CONTACT WITH ONE ANOTHER, COMPRISING THE STEPS OF: A. PRODUCTING A CLOUD OF ELECTROSTATICALLY CHARGED SOLID PARTICLES OF HEAT-FUSIBLE RESINOUS MATERIAL, B. EXPOSING SAID WORKPIECE TO SAID CHARGED PARTICLES WITH SAID WORKPIECE CHARGED EFFECTIVELY OPPOSITE THERETO TO CAUSE A LAYER OF SAID PARTICLES TO DEPOSIT UPON SAID FIRST AND SECOND ZONES THEREOF, C. HEATING SAID FIRST ZONE OF SAID WORKPIECE TO A RELATIVELY HIGH TEMPERATURE ABOVE AMBIENT WHILE SIMULTANEOUSLY COOLING SAID SECOND ZONE THEREOF TO CAUSE AT LEAST PARTIAL FUSION AND COHEREHCE OF SAID PARTICLES ON SAID FIRST ZONE WHILE MAINTAINING SAID SECOND ZONE AT A RELATIVELY LOWTEMPERATURE SUBSTANTIALLY BELOW SAID RELATIVELY HIGH TEMPERATURE TO SUBSTANTIALLY PREVENT FUSION AND COHERENCE OF PARTICLES ON SAID SECOND ZONE TO THEREBY FACILITATE REMOVAL THEREFORM, D. THEREAFTER REMOVING FROM SAID SECOND ZONE ANY OF SAID PARTICLES OF RESINOUS MATERIAL REMAINING THEREON, SAID SIMULTANEOUS HEATING AND COOLING STEP PRODUCING A RELATIVELY STEEP TEMPERATURE GRADIENT BETWEEN SAID FIRST AND SECOND ZONES SO THAT THE MARGINS OF SAID LAYER OF PARTICLES ON SAID FIRST ZONE ARE RELATIVELY SHARPLY DEFINED.
 2. The method of claim 1 additionally including the step of heating said workpiece subsequent to said simultaneous heating and cooling step to at least about the melting point of said resinous material to melt said particles thereof and to produce a unified and adherent coating upon said first zone of said workpiece.
 3. The method of claim 1 additionally including the step of removing a portion of said layer of particles deposited upon said first zone of said workpiece prior to said simultaneous heating and cooling step.
 4. The method of claim 1 additionally including the step of removing said layer of particles deposited upon said second zone of said workpiece prior to said simultaneous heating and cooling step.
 5. The method of claim 1 wherein said resinous material is a synthetic thermoplastic resin.
 6. The method of claim 1 wherein said workpiece is an armature rotor having a cylindrical core portion with axially extending slots about the circumference thereof, the surfaces of said slots comprising said first zone of said workpiece.
 7. A method for the production of a unified, adherent coating of heat-fusible material upon only a portion of a work-piece having proximate first and second zones in heat-conductive contact with one another, comprising the steps of: a. producing a cloud of electrostatically charged solid particles of heat-fusible resinous material; b. exposing said workpiece to said charged particles with said workpiece at about ambient temperature and charged effectively opposite to said particles to cause a layer thereof to deposit upon said first and second zones of said workpiece; c. thereafter heating said first zone of said workpiece to a relatively high temperature above ambient while simultaneously cooling said second zone thereof to cause at least partial fusion and coherence of said particles on said first zone while maintaining said second zone at a relatively low temperature substantially below said relatively high temperature to substantially prevent fusion and coherence of particles on said second zone to thereby facilitate removal therefrom; and d. thereafter removing from said second zone any of said particles of resinous material remaining thereon, said simultaneous heating and cooling step producing a relatively steep temperature gradient between said first and second zones, so that the margins of said layer of particles on said first zone are relatively sharply defined, said step (d) being effected immediately after said step (c).
 8. The method of claim 7 additionally including the step of heating said workpiece subsequent to said simultaneous heating and cooling step to at least about the melting point of said resinous material to melt said particles thereof and to produce a unified and adherent coating upon said first zone of said workpiece.
 9. The method of claim 7 additionally including the step of removing a portion of said layer of particles deposited upon said first zone of said workpiece prior to said simultaneous heating and cooling step.
 10. The method of claim 7 additionally including the step of removing said layer of particles deposited upon said second zone of said workpiece prior to said simultaneous heating and cooling step.
 11. The method of claim 7 wherein said resinous material is a synthetic thermoplastic resin.
 12. The method of claim 7 wherein said workpiece is an armature rotor having a cylindrical core portion with axially extending slots about the circumference thereof, the surfaces of said slots comprising said first zone of said workpiece. 